TUBITAK Project, 2015 - 2016
Fish passes are structures that facilitate the upstream or downstream migration of aquatic organisms over obstructions to migration such as dams and weirs. The function of a fish passage structure is to provide favorable hydraulic conditions (sufficient flow depth, large enough and well-spaced resting areas, low local flow velocities, and low turbulent flows) for fishes to migrate through upstream direction.
Under the scope of the proposed project, the hydraulic characteristics of the brush-type fish pass, which has a different working principle than conventional fish passes (pool-weir, vertical slot, natural type), will be experimentally investigated. In brush-type fish pass, the brush elements do not totally block the flow and hydraulic elements have permeability. A quasi-uniform flow condition occurs and flow regime is subcritical. The energy dissipation is rather effective because the large number of bristles produce many small eddies which initiate strong energy consumption by the viscosity of the water. The usual process of energy cascade process, appearing with large roughness elements, generating the phases generation of shear zones – large eddies – smaller eddies – finally energy dissipation by viscosity in the smallest eddies - is shortened, because only the last two steps dominate.
For the proposed project, it is aimed to construct a 1:3 scale physical model of the brush-type fish pass and carry out systematic measurements on the model. The bristles will be manufactured form polypropylene having a diameter of 2 mm and a length of 160 mm. The experiments will be conducted in a rectangular 0.4 m wide recirculating flume. The experiments will be carried out for 3 different bed slopes (%2, %4, and % 6). For each bed slope, the data will be gathered for 6 different relative submergence and 4 different brush density. The densities of the brushes will be adjusted by changing the stream-wise and lateral distances of the brush blocks; whereas relative submergences will be controlled by changing the discharge. Moreover, local flow velocities will me measured in the gap regions by micro propeller and velocity profiles will be obtained. The model test results will be transferred to the prototype based on the Froude similitude.
The model test results will be expected to contribute the understanding the hydraulic conditions of the brush-type fish pass. Because, the literature lacks from a systemic experimental study on brush-type fish passage structures. Based on the experimental data and analysis, a new dimensioning and hydraulic design concept is expected to be developed by using dimensionless numbers. Unlike previous studies, macro-roughness conditions will be referred to with two parameters as relative submergence and density of brush elements in the plan projection. Accordingly, it is aimed to relate the Darcy-Weisbach friction factor with the relative submergence and density of the brush elements. By using the proposed formula, average velocity and discharge can be estimated for the given uniform flow depth and channel geometry data. Consequently, the model test results will be also compared with the conventional fish passage structures.